In recent years, a light source-sensor integrated type photoelectric conversion device used in a sensor which irradiates a living body with light, and detects its response, a sensor which optically detects a surface state of a display device, and the like has been proposed.
For example, a light source integrated type solid-state imaging device has been proposed as a document reading device of a copying machine. In this solid-state imaging device, a thin-film light-emitting element and a solid-state imaging element (light-receiving element) are independently formed on non-overlapping regions on a substrate. An object is irradiated with light from the light-emitting element, which is extracted on the side opposite to the substrate, and reflected light from the object is detected by the light-receiving element. Since the light-emitting element and light-receiving elements are formed on a single substrate, a state of the object can be accurately detected.
However, in the device of this type, since the light-emitting element and light-receiving element are independently formed on the substrate, their structures are restricted, and much labors are required to manufacture the device. For example, when the light-emitting element is formed after the light-receiving element is formed, an upper layer of the already formed light-receiving element may be damaged upon formation of the light-emitting element, resulting in deterioration of element characteristics. Especially, this problem is conspicuous when organic semiconductor materials are used. Furthermore, when the light-emitting element and light-receiving element are formed on the single substrate, some light rays from the light-emitting element are reflected by respective layers in the device, and enter the light-receiving element, thus causing an increase in detection noise.
As a near-infrared spectroscopy which irradiates a living body with near-infrared light and detects its response to obtain information in the living body, for example, a pulse oximeter has been put into practical use. However, near-infrared light in the living body is easier to be transmitted than visible light, but it is largely scattered. Hence, an amount of reflected light is several percentages or less with respect to incident light. Therefore, detection at a high sensitivity is required. However, in a PIN photodiode of microcrystalline Si, which is popular as a light-receiving element, it is insufficient to obtain a light-receiving element which has a high sensitivity to near-infrared light in terms of a band gap.